JavaScript Function.prototype.call() Method (original) (raw)
Last Updated : 24 Jan, 2022
The call() method allows function calls belonging to one object to be assigned and it is called for a different object. It provides a new value of this to the function. The call() method allows you to write a method once and allows it for inheritance in another object, without rewriting the method for the new object.
Syntax:
myFunc.call([thisArg[, arg1, arg2, ...argN]])
Parameters:
- thisArg: The values to use as this when calling myFunc function.
- arg1, arg2, …, argN: These are the arguments for the above mentioned function.
Note: In certain cases, thisArg may not be the actual value. If the method is in non-strict mode, primitive values will be converted to objects and null,undefined will be replaced with the global object.
Return value: It returns the specified this value and arguments as a result of calling of the function.
Example 1: The following example demonstrates the use of calling to chain constructors for an object.
html
< script >
function Product(name,
`` price) {
`` this.name = name;
`` this.price = price;
`` }
`` function Vehicle(name,
`` price) {
`` Product.call(this,
`` name, price);
`` this.category = 'vehicle';
`` }
`` function Restaurant(name,
`` price) {
`` Product.call(this,
`` name, price);
`` this.category = 'restaurant';
`` }
`` const car = new Vehicle('Suzuki',
`` 100000);
`` const restau = new
`` Restaurant('KFC', 1000);
`` console.log(car);
`` console.log(restaurant);
</ script >
Output:
Example 2: The following example demonstrates the use of call() method to invoke an anonymous function.
html
< script >
const Birds = [
`` { species: 'Pigeon', name: 'King' },
`` { species: 'Crow', name: 'Fail' }
`` ];
let i=0;
`` while(i< Birds.length ){
`` (function(i) {
`` this.print = function () {
`` console.log('#' + i + ' '
`` + this.species
`` + ': ' + this.name);
`` }
`` this.print();
`` }).call(Birds[i], i);
`` ++i;
`` }
</script>
Output:
#0 Pigeon: King #1 Crow: Fail
Example 3: The following example demonstrates the use of call method to invoke a function and specifying the context for ‘this’.
html
< script >
function greet() {
`` const reply = [this.animal,
`` 'typically sleep between',
`` this.sleepDuration].join(' ');
`` console.log(reply);
`` }
`` const obj = {
`` animal: 'Rats',
`` sleepDuration: '2 and 5 hours'
`` };
`` greet.call(obj);
</ script >
Output:
Rats typically sleep between 2 and 5 hours
Example 4: The following example demonstrates the use of call() method to invoke a function without specifying the first argument.
html
< script >
var str = 'Brad';
function display() {
`` console.log('string value is %s ',
`` this.str);
}
display.call();
</ script >
Output:
string value is Brad
Note: In strict mode, the value of this will be undefined.
html
< script >
'use strict';
var str = 'Brad';
function display() {
`` console.log('str value is %s ',
`` this.str);
}
display.call();
</ script >
Output:
Cannot read property 'str' of undefined